Geographic variation in the structure and complexity of vocalizations has been widely reported for birds (Baker & Cunningham 1985, Kroodsma 2004) and, to a lesser extend, for pinnipeds (Sanvito & Galimberti 2000, Terhune et al. 2008), cetaceans (Weilgart & Whitehead 1997, Deeke et al. 2000, Noad et al. 2000), primates (de la Torre & Snowdon 2009) and bats (Russo & Jones 1999, Davidson & Wilkinson 2002). Geographic variation of vocalizations is often caused by vocal learning but this relation is not mandatory (Janik & Slater 1997, Boughman & Moss 2003). In bats, there is currently no evidence for geographic variation of vocalizations through vocal learning. Pups of the greater sac-winged bat Saccopteryx bilineata learn an adult vocalization type, the territorial song, through the imitation of tutors (Knörnschild et al. 2009). We are investigating whether territorial songs differ between various populations in Costa Rica. We will map the acoustic distance in signal space (i.e., difference between territorial songs from different populations) onto the genetic and geographic distance in order to determine whether acoustic differences between populations (Davidson & Wilkinson 2002) are caused by genetic and/or geographic isolation or by vocal learning. We will gather data at two different levels: on the colony level (by sampling all known one-harem and multi-harem colonies at two sites in Costa Rica) and on the population level (by sampling 1-2 colonies each at 10 sites all over Costa Rica).

Syntax in Courtship Songs and Babbling Bouts of Saccopteryx bilineata

Syntax is defined as a set of rules for assembling units of any type into a larger unit, e.g. the temporal arrangements of acoustic units within song (Marler 1977). As a prerequisite for using combinatorics (“making infinite use of finite means''), the advantages of syntax are best illustrated in the vast expressive power of human language (Chomsky 1965, Jackendoff 1997). Hence, the transition from non-syntactic to syntactic communication was a keystone in the evolution of human language (Nowack 1999; Hauser et al. 2002, Fitch 2005) because syntax allows larger repertoires and the possibility to formulate new messages (Nowak et al. 2000). One can distinguish between ‘phonological’ and ‘lexical’ syntax (Marler 1977, Jackendoff, 1999), with phonological syntax referring to the rules that define the assembly of smaller vocal units into larger ones, and lexical syntax tothe corresponding changes in meaning. Phonological syntax is frequently observed in animal communication, especially in the learned songs of birds (Kroodsma & Miller 1982, Marler 1984) and whales (Payne & Payne 1985, Noad et al. 2000) or the calls of primates (Clarke et al. 2006, Crockford & Boesch 2005), whereas the evidence for lexical syntax is rather scarce (Kako 1999, Zuberbühler 2002). At least in birds (Balaban 1988, Honda & Okanoya 1999), the complexity and diversity of song syntaxes can evolve through sexual selection if females prefer complex songs. In bats, little evidence for phonological syntax exists (Kanwal et al. 1994, Esser et al. 1997), even though it is probably fairly widespread, especially in species with complex vocal repertoires. The greater sac-winged bat Saccopteryx bilineata is well suited for studying syntax in bat vocalizations because its vocal repertoire is well described, complex and consists mainly of multi-syllabic vocalization types that are uttered in distinct social contexts (Bradbury & Emmons 1974, Behr & von Helversen 2004, Knörnschild et al. 2008) and are acquired through vocal learning (Knörnschild et al. 2006, Knörnschild et al. 2009).
Male S. bilineata produce long and complex courtship songs consisting of various distinct syllables. The repertoire size of the most common syllable type, the trill, differs between males and is positively correlated with male reproductive success, indicating that female S. bilineata prefer songs with highly variable trill syllables (Behr & von Helversen 2004). Based on this finding, we want to investigate the structural rules underlying the whole courtship songs, i.e. determining whether the sequence of syllables in courtship songs is defined through syntax or random improvisation. In order to do this, we will analyse courtship songs of numerous male S. bilineata that were gathered over several years. We will try to link the assessed complexity of courtship song performance to male reproductive success.
In S. bilineata, pups of both sexes produce long babbling bouts during the acquisition of the vocal repertoire. In these babbling bouts, adult vocalization types are combined into supposedly meaningless strings of vocalizations (Knörnschild et al. 2006). We will investigate whether babbling is defined by syntactical rules and whether these rules change as babbling bouts become more complex throughout the pups’ ontogeny. 

Balaban E. 1988. Proc Natl Acad Sci USA 85:3657-3660 / Behr O, von Helversen O. 2004. Behav Ecol Sociobiol 56: 106-115 / Bradbury JW, Emmons L. 1974. Z Tierpsych 36: 137-183 / Bradbury JW, Vehrencamp SL. 1977. Behav Ecol Sociobiol 2: 1-17 / Chomsky N. 1965. Aspects of the Theory of Syntax. MIT Press, Cambridge / Clarke E, Reichard UH, Zuberbühler K. 2006. Plos ONE 1:e73 / Crockford C, Boesch C. 2005. Behaviour 142:397-421 / Esser KH, Condon CJ, Suga N, Kanwal JS. 1997. Proc Natl Acad Sci USA 94:14019-14024 / Fitch WT. 2005. Biol Philos 20:193-230 / Hauser M., Chomsky N. and Fitch W.T. 2002. Science 298:1569-1579 / Honda E, Okanoya K. 1999. Zool Sci 16:319–326 / Jackendoff R. 1977. The Architecture of the Language Faculty. MIT Press, Cambridge / Jackendoff R. 1999. Trends Cogn Sci 3:272-279 / Kako E. 1999. Anim Learn Behav 27:1-14 / Kanwal JS, Matsumura S, Ohlemiller K, Suga N. 1994. JASA 96:1229-1254 / Knörnschild M, Behr O, von Helversen O. 2006. Naturwissenschaften 93:451-454 / Knörnschild M, von Helversen O, Mayer F. 2008. Anim Behav 76:1001-1009 / Knörnschild M, Nagy M, Metz, M, Mayer F, von Helversen O. 2009. Biol Lett 5(6) / Kroodsma DE, Miller EH. 1982. Acoustic communication in birds: Volume 2. Academic Press, New York / Marler P. 1977. Recognition of complex acoustic signals (Ed. by T Bullock). Dahlem Konferenzen, Berlin / Noad MJ, Cato DH, Bryden MM, Jenner MN, Jenner KCS. 2000. Nature 408:537 / Nowak MA, Krakauer DC. 1999. Proc. Natl Acad. Sci. USA 96:8028-8033 / Nowak MA, Plotkin JB, Jansen VAA. 2000. Nature 404:495-498 / Payne K, Payne R. 1985. Z Tierpsychol 68: 89-114 / Zuberbühler, K. 2002. Anim Behav 63:293-299